Commitments and Contingencies (Details) $ in Millions	9 Months Ended
Sep. 30, 2016 USD ($)
Natural Gas Supply Commitments [Member]
Recorded Unconditional Purchase Obligation Payment Schedule [Abstract]
2016	$ 132
2017	454
2018	455
2019	267
2020	124
After 2020	133
Minnesota Service Territory [Member]
LegalEnvironmentalAndOtherRegulatoryMattersLegalMattersGasMarketManipulationCasesAbstract
Accrual for Environmental Loss Contingencies	7
Minnesota Service Territory [Member] \| Maximum [Member]
LegalEnvironmentalAndOtherRegulatoryMattersLegalMattersGasMarketManipulationCasesAbstract
Estimated remediation costs for the Minnesota sites	$ 29
Site Contingency, Years to Resolve Contingency	50 years
Minnesota Service Territory [Member] \| Minimum [Member]
LegalEnvironmentalAndOtherRegulatoryMattersLegalMattersGasMarketManipulationCasesAbstract
Estimated remediation costs for the Minnesota sites	$ 4
Site Contingency, Years to Resolve Contingency	30 years
GenOn Demand Charges Transportation Contracts [Member]
LegalEnvironmentalAndOtherRegulatoryMattersLegalMattersGasMarketManipulationCasesAbstract
Guarantee of Affiliate Senior Notes	$ 15
Enable Guaranteed Senior Notes [Member]
LegalEnvironmentalAndOtherRegulatoryMattersLegalMattersGasMarketManipulationCasesAbstract
Guarantee of Affiliate Senior Notes	$ 1,100

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Estimate of the reasonably possible loss exposure at an individual site.

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Total costs accrued as of the balance sheet date for environmental loss contingencies.

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Minimum amount of purchase arrangement maturing after the fifth fiscal year following the latest fiscal year. Includes, but not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

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Minimum amount of purchase arrangement maturing in the fourth fiscal year following the latest fiscal year. Includes, but not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

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Minimum amount of purchase arrangement maturing in the second fiscal year following the latest fiscal year. Includes, but not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

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Minimum amount of purchase arrangement maturing in the remainder of the fiscal year following the latest fiscal year ended. Includes, but is not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

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